Single-frequency detectors use one fixed frequency, which is not ideal for conductive products with high salt or moisture content. In these applications, product effect can cause more false positives. Lowering the frequency can reduce product effect, but it also weakens the metal signal. This means the detectable metal contaminants must be larger than they would need to be in dry, non-conductive products.

Multi-Simultaneous Frequency detectors use multiple frequencies in parallel. By inspecting products with both low and high frequencies simultaneously and using a smart algorithm to remove the product signal, these metal detectors can virtually eliminate false rejects. This technology represents a major advancement in metal detection, especially for applications challenged by product effect or metallized film packaging. It helps reduce the risk of false rejects while maintaining the sensitivity needed to detect small metal fragments.

Compliance is guided by frameworks such as HACCP (Hazard Analysis and Critical Control Points), the U.S. FDA requirements under FSMA (Food Safety Modernization Act), and EU regulations. It is also guided by GFSI-recognized standards and applicable retailer codes of practice. Depending on the risk assessment and food safety plan, metal detection may be designated as a Critical Control Point (CCP). In such cases, documented procedures are typically required for sensitivity checks, routine testing with certified test pieces, validation and verification, and record-keeping to demonstrate that the system is consistently effective.

Stainless steel is non-magnetic and a poor conductor of electricity, which makes it one of the most difficult metals to detect. This is especially true in wet or conductive products such as cheese or frozen products with high moisture content. Because the stainless steel signal is weaker, product effect can mask it, making it harder to detect smaller contaminants. Multi-Simultaneous Frequency technology, when combined with a smart algorithm and Product Signal Suppression technology, can improve performance by significantly reducing product effect. This creates a clearer metal signal, particularly for stainless steel, and helps the detector operate at higher overall sensitivity. As a result, the metal detection system can more easily detect smaller stainless steel pieces, including wire and swarf.

Metal detection and x-ray inspection are complementary technologies. Metal detectors are generally the best choice for detecting metal contaminants, especially in many dry products, although specialized metal detectors can also perform well in wet or product-effect applications. X-ray systems can detect other physical contaminants such as glass, stone, and bone, and can also perform additional quality checks such as mass measurement and package integrity inspection.

Manufacturers are increasingly using both technologies at different points on the production line as they each address different risks; this helps them build a more comprehensive contamination-control program. A combined approach, often guided by a HACCP risk assessment, provides a robust program for physical contamination control.

The return on investment (ROI) of a metal detection system is influenced by several factors, including: 

• Risk reduction through avoiding costly recalls or brand-damaging incidents
• Reduced product waste from fewer false rejects
• Improved operational efficiency from less downtime
• Compliance-related savings from smoother audits

A system that delivers these benefits over many years, especially in harsh environments, can also contribute to a higher ROI.